I don't work for BA, so my information is third-hand, but as I understand it the reasons are historical.
Originally, in the early 70's, training was completed at Hamble where a selected number of cadets went through their zero-to-hero training program. Along the way of each program a good % of these cadets dropped out/failed to meet their required standards - which were high. So since this time an integrated student approach to co-pilot training has been inherent in their culture - only nowadays they have simply delegated this approach to a few selected schools.
Unfortunately, FL370 Officeboy's post contains grains of reality, especially for the UK, where regardless of the training route you take it simply is not a good time to be training. However, the gloss of the FTO's and the subtle suggestions that "there's light at the end of the tunnel", "some airlines are talking about pilot shortages in 2 years" and "by the time you finish there'll be jobs around" etc... are only ways of drawing new revenue into the industry.
Be warned, integrated FTOs have very well honed sales cultures and are probably quite happy to flout and breach consumer law including the law of misrepresentation in order get ya money. So plan carefully, invest for the long term and avoid "I want a job NOW" fast-tracking mentality as a great many of you will be very sorely dissappointed.
